Recently, introduction of touch panel systems to various kinds of electronic devices has been growing rapidly. For example, the touch panel systems are introduced to portable information devices such as smartphones and automatic vending machines such as automatic ticket machines.
The touch panel system is typically configured to include (i) a display device and (ii) a touch panel stacked on an upper side (front surface) of the display device. Therefore, a sensor provided on the touch panel is likely to be affected not only by a noise such as a clock generated in the display device but also by other noises coming from the outside. Such the noises lead to impairment in detection sensitivity for a touch operation.
Patent Literature 1 describes a touch panel system (coordinates input device) including a countermeasure against such noises. The touch panel system of Patent Literature 1 includes a noise processing section for removing a noise. FIG. 19 is a block diagram illustrating a noise processing section 100 included in the touch panel system of Patent Literature 1. As shown in FIG. 19, the noise processing section 100 includes a filter section 101, a logical inversion section 102, and an adding section 103. The filter section 101 receives an output signal (analog signal) from a sensor provided in a touch panel (not illustrated). The filter section 101 extracts, as a noise signal, an AC signal component included in the input signal. The logical inversion section 102 inverts by 180° the phase of the noise signal thus extracted. The adding section 103 adds, to the input signal which is supplied to the filter section 101 and which includes the noise signal, the noise signal whose phase has been inverted by 180°.
Thus, according to the touch panel system of Patent Literature 1, the noise signal extracted by the filter section 101 is inverted, and the signal thus inverted is added to the input signal (analog signal) supplied from the sensor. Namely, to the noise component included in the input signal supplied from the sensor, such a signal is added which has the same level as the noise component and whose phase has been inverted. This cancels the noise superimposed on the input signal supplied from the sensor. This makes it possible to reduce effects given by the noise included in the input signal supplied from the sensor.
Meanwhile, Patent Literature 2 discloses a capacitance value distribution detection circuit that detects a distribution of capacitance values of a plurality of capacitances, which capacitances are each formed at intersections of a plurality of first signal lines with a plurality of second signal lines. As shown in FIG. 1 of Patent Literature 2, a positional relationship of (i) drive lines for driving the touch panel with (ii) sense lines for reading out signals from the touch panel is fixed with respect to the touch panel.
FIG. 41 is a block diagram illustrating a configuration of a conventional touch panel system 91. FIG. 42 is a schematic view illustrating a configuration of a touch panel 93 provided in the touch panel system 91. The touch panel system 91 includes the touch panel 93 and a capacitance value distribution detection circuit 92. The touch panel 93 includes drive lines HL1 to HLM arranged parallel to each other in a horizontal direction, sense lines VL1 to VLM arranged parallel to each other in a vertical direction, and capacitances C11 to CMM each formed at intersections of the drive lines HL1 to HLM with the sense lines VL1 to VLM.
The capacitance value distribution detection circuit 92 includes a driver 95. The driver 95 applies a voltage to the drive lines HL1 to HLM in accordance with a code sequence, to drive the capacitances C11 to CMM. The capacitance value distribution detection circuit 92 includes a sense amplifier 96. The sense amplifier 96 reads out, via the sense lines VL1 to VLM, a linear sum of voltages corresponding to the capacitances C11 to CMM driven by the driver 95, and supplies this linear sum of voltages to an A/D converter 98. The A/D converter 98 converts, from analog to digital, the linear sum of voltages corresponding to the capacitances, read out via the sense lines VL1 to VLM, and supplies the converted linear sum to a capacitance value distribution calculation section 99.
The capacitance value distribution calculation section 99 calculates a capacitance value distribution on the touch panel 93 based on (i) the linear sum of voltages corresponding to the capacitances, supplied from the A/D converter 98, and (ii) the code sequence, and supplies the calculation result to a touch recognition section 90. The touch recognition section 90 recognizes a position touched on the touch panel 93 based on the capacitance value distribution supplied from the capacitance value distribution calculation section 99.
The capacitance value distribution detection circuit 92 includes a timing generator 97. The timing generator 97 generates a signal specifying an operation of the driver 95, a signal specifying an operation of the sense amplifier 96, and a signal specifying an operation of the A/D converter 98, and supplies these signals to the driver 95, the sense amplifier 96, and the A/D converter 98, respectively.